Field of the Invention
The present invention relates to a manufacturing method of an avalanche photodiode capable of improving the activation rate of the carbon added to the p-type field relaxation layer.
Background Art
In electronic devices and optical devices requiring a local high-density p-type semiconductor layer, carbon with low diffusion is often used as a dopant. However, since hydrogen is taken into a crystal at carbon doping, there is a problem of lowering of a carbon activation rate. On the contrary, in electronic devices represented by hetero bipolar transistors, by performing annealing in a furnace during crystal growth, the activation rate of a carbon dope layer can be improved, and favorable characteristics and reliability can be obtained (see Japanese Patent Laid-Open No. 2000-68284 and H. Ito et al., Jpn. J. Appl: Phys. Vol. 35 (1996), pp. 6139 to 6144, for example).
On the other hand, as an example in which the carbon dope layer is used in the optical device, an electron multiplication type avalanche photodiode with low noise and high sensitivity has been realized (see IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 20, NO. 6, Mar. 15, 2008, for example). In order to control an avalanche mode, a p-type AlInAs field relaxation layer doped with carbon at high density is used, and it indicates superiority over the doping of Zn or Be which is a general p-type dopant in terms of characteristics. However, there is a concern that the lowered activation rate of carbon in the field relaxation layer caused by hydrogen in the carbon dope layer deteriorates reliability. Thus, in order to improve the activation rate of the p-type semiconductor layer doped with carbon, a sequence for growing an InGaAs light absorbing layer at a high temperature after growth of the field relaxation layer is preferable. For example, as illustrated in FIG. 6, execution of annealing can be considered between the growth of the field relaxation layer and the growth of the light absorbing layer. At this time, it is preferable that heat damage at temperature rise is relaxed by covering a surface of the field relaxation layer by InGaAs or InGaAsP (see Japanese Patent Laid-Open No. 2014-99467, for example).